In the airlay web forming process in use by E.I. du Pont de Nemours and Company (DuPont) in the manufacture of spunlaced fabrics sold under the trademark Sontara.RTM., fiber is carried by a relatively fast-moving air stream to a screen conveyor forming a web of randomly arranged fibers. The commercial process is disclosed and described in U.S. Pat. No. 3,797,074 to Zafiroglu.
Upon investigation, it has been hypothesized that the air flow which carries the fiber to the screen conveyor is subject to eddies, vortices and other indicators of turbulence at the peripheral sides of the web which is undesirable. In accordance with Zafiroglu, the air that is used to carry the fiber is introduced through a system of large conduits and fans. Prior to receiving the fiber, the air flow is directed through screens and straighteners to provide a uniform flow substantially free of large-scale turbulence and vortices. Thereafter, the large volume, relatively slow-moving air flow is accelerated through a converging section or nozzle into a reduced cross sectional area conduit which is substantially flat and wide to be suited for laying down a wide web. It is believed that the acceleration nozzle of Zafiroglu creates, or allows the creation of the vortices and turbulence at the peripheral sides of the web which is believed responsible for certain defects.
U.S. Pat. 5,564,630 to Giles et al (assigned to DuPont) is directed to an improved nozzle over that of Zafiroglu by providing smoothly curving, low angle peripheral walls. The nozzle is particularly helpful in reducing edge defects which can result from vortices and turbulence. Regardless, considerable need remains for improvement of web properties.
U.S. patent application Ser. No. 08/760,119 now abandoned (also assigned to DuPont) is directed to combining the advantages of feeding carded fibers to an airlay. The air stream in that patent application is controlled by use of fans and a series of filters and air straighteners to create a laminar air flow. However, such an arrangement may present disadvantages in terms of space requirements and by making the maintenance of the cards especially difficult.